Particulate Matter (PM 10 ) In the period 1997-2008, 18-50 % of the urban population was potentially exposed to ambient air concentrations of particulate matter (PM 10 ) in excess of the EU limit value set for the protection of human health (50 microgram /m 3 daily mean not be exceeded more than 35 days a calendar year); (Figure 1). Nitrogen dioxide (NO 2 ) In the period 1997-2008, 6-41 % of the urban population was potentially exposed to ambient air nitrogen dioxide (NO 2 ) concentrations above the EU limit value set for the protection of human health (40 microgram NO 2 /m 3 annual mean). There was a slight downwards trend over the period (Figure 1). Ozone (O 3 ) In the period 1997-2008, 13-62 % of the urban population in Europe was exposed to ambient ozone concentrations exceeding the EU target value set for the protection of human health (120 microgram O 3 /m 3 daily maximum 8-hourly average, not to be exceeded more than 25 times a calendar year by 2010). The 62 % of the urban population exposed to ambient ozone concentrations over the EU target value was recorded in 2003, which was the record year. There was no discernible trend over the period (Figure 1). Sulphur dioxide (SO 2 ) In the period 1997-2008, the fraction of the urban population in EEA-32 member countries that is potentially exposed to ambient air concentrations of sulphur dioxide in excess of the EU limit value set for the protection of human health (125 microgram SO 2 /m 3 daily mean not to be exceeded more than three days a year), decreased to less than 1 %, and as such the EU limit value set is close to being met everywhere in the urban background (Figure 1).

Peder Jensen, EEA transport and the environment expert.
Transport is harmful to the environment in many different ways. The most visible effect of transport is some of the emissions that we see: we can see the exhaust gas coming out of a car and at certain times it's very dirty and very dark. It's a very visible way where it's harming the environment, harming the air that we are all breathing. But there are also effects that are not quite so visible - when we are burning fuel in our engines we are emitting a lot of different gases and some of them are invisible greenhouse gases that help trap the heat in the atmosphere to get the earth to go warmer.
One of the other important effects of transport is the noise impact. Noise means that people have a hard time sleeping, that they therefore don't get the rest that they need. It also affects the animals, disturbs their life, if roads or railroads run through nature areas it therefore means a reduced quality of life for both animals and people.
Finally, transport infrastructure has a tendency to fragment natural habitats for animals. Lots of animals are disturbed by roads, they cannot cross the road, they are either scared off by the noise or they can't find ways to cross these different infrastructures and this means that the habitats they are living in don't work so well for their reproduction.

The rationale for selection of pollutant and corresponding limit/target values for CSI 004 is given in the justification for indicator selection. Only urban and sub-urban background monitoring stations have been included in the calculations. Data for Cyprus, Greece and Malta, are not included due to the geographical coverage of the Urban Audit.